Emergency vehicles use sirens and flashing lights to warn other drivers of their approach or of their presence. There are many reasons why sirens and flashing lights do not provide adequate warnings. Flashing lights can only be seen where there is a direct line of sight and cannot be seen around corners in built-up metropolitan areas. Sirens cannot heard by people who are hard of hearing or in vehicles where there is competing noise, such as a loud radio or noisy machinery or a different emergency vehicle that has its siren on. Frequent collisions between emergency vehicles and other vehicles or even between two emergency vehicles responding to a call indicate that a siren or flashing lights alone are not adequate to warn all drivers of the presence or approach of the emergency vehicle. The consequences of a driver straying into the path of a rapidly moving emergency vehicle are so severe that there is a need for some additional way to warn drivers of the presence or approach of an emergency vehicle.